Cache npath data so we don't keep creating stuff over and over again

Author: shana

src/GitHub.Api/IO/NiceIO.cs

@@ -753,11 +753,14 @@ public static NPath HomeDirectory
             }
         }
 
+        private static NPath systemTemp;
         public static NPath SystemTemp
         {
             get
             {
-                return new NPath(FileSystem.GetTempPath());
+                if (systemTemp == null)
+                    systemTemp = new NPath(FileSystem.GetTempPath());
+                return systemTemp;
             }
         }